This invention relates to a circuit in which the output circuit and the input circuit, which includes an operational amplifier, are electrically isolated.
Many different kinds of full wave rectifying circuits are known. However, in all of these there was a circuit design limitation in the range of the level variation between the output and input voltages. Accordingly, the applicability of these circuits was circumscribed.
In order to solve this problem, a full wave rectifying circuit, which electrically isolates the input and output using a dual polarity photocoupler, has been proposed. However, in this kind of circuit, there is a decrease in the output voltage due to the forward voltage Vf of the light-emitting diode, which becomes the source of output error.
Also, function generators are known, which produce function curves, such as a voltage-current characteristic curve. In general, function generators are constructed of a plurality of limiter circuits. However, in the various prior art function generators the input and output circuits were electrically connected so that they had to be operated at the same voltage. This results in a complicated circuit structure.